Cascade refrigeration systems generally include a first side cooling cycle, or a high side cycle, and a second side cooling cycle, or a low side cooling cycle. The two cooling cycles interface through a common heat exchanger, i.e., a cascade evaporator/condenser. The cascade refrigeration systems may provide cooling at very low temperatures in an efficient manner.
The compressors in these cooling cycles of a cascade refrigeration system generally require a source of oil in communication with the flow of refrigerant therein. Any oil that may be trapped in the refrigerant vapor downstream of the compressors then may be removed via an oil separator and the like. Periodic recovery of the compressor oil also may be required. This oil recovery may be performed automatically on the low side cycle but manual draining may be required on the high side cycle due to the high pressures involved. Such manual oil recovery may be expensive and inefficient.
There is thus a desire for refrigeration systems such as cascade refrigeration systems with improved oil recovery systems. Preferably such improved oil recovery systems may provide full oil recovery in a high side cooling cycle in an efficient manner without the use of manual techniques or the use of complex or expensive mechanisms.